High speed diesel engines, particularly those used to power vehicles, are required to operate efficiently and with low emissions over a wide range of loads and engine speeds. They are expected to operate smoothly and cleanly at low idle speed conditions with a very small quantity of fuel injected into each cylinder each cycle. The same engines are also expected to run cleanly and efficiently at several thousand injections per minute with large enough quantities of fuel delivered at each injection cycle to utilize air charges at high density as supplied by turbochargers.
To achieve acceptable performance and emission standards, each fuel injection valve on such engines must be not only highly responsive but as identical in delivery characteristics to others of its set as is economically feasible.
Compact injection valve designs suitable for diesel engines employ helical compression springs made of high strength wire having a high modulus of elasticity in torsion. Such springs are needed to provide high unseating force and high spring rate in small size so they can be fitted in a limited space and hot environment with required reliability.
Such is the state of the art in spring design and manufacturing processes that compression springs cannot be made in quantity at reasonable cost with uniformly parallel ends. Even more difficult to produce are springs whose ends will remain parallel without external restraint when compressed by on-axis forces. Furthermore, variations are sizable in coil diameter, in length unassembled, in exact number of active coils and in tightness of closure of end coils when made by the best production methods. Means must be provided for adjustment of the length of springs as assembled if the assembled load is to be accurately controlled. The rate at which springs deflect for added increments of load also vary appreciably between individual springs out of a production run.
Another requirement is economy of servicing. The servicing cost will be low if the parts likely to require replacement are low in cost but only if little or no skilled labor is required to replace them. A fixture and method for assembling and standardizing embodiments of fuel injection valves for internal combustion engines and more particularly to compact, highly responsive injection valves with the high uniformity of characteristics required for use in high speed diesel engines for use in applications requiring high performance and compliance with stringent emission regulations. This invention is also particularly applicable applicable to fuel injection valves employing highly compact compression springs of helically coiled high strength wire located close to the movable valve to provide the force needed to hold the valve on its seat between injections. Such a spring is highly stressed and should be very stiff for its size to enable it to move the valve with high responsiveness to pressure changes.
The fixture is for use in combination with an embodiment of valve which includes a load transmitting connection between one end of the compression spring and the movable valve that allows that end of the spring to tip relative to the valve by rolling, not sliding, of one loaded surface on another. One surface is a central portion of one side of a cylindrical hole through the center line of the valve member adjacent the free end of the spring. The other surface is on the surface of a hardened steel pin of smaller diameter than the opening in the valve member through which it is inserted for load bearing contact. The pin acts as a beam with its outer ends loaded by the force of the compressed spring.
Other embodiments of the valve utilize the tendency of a ball held axially in a high velocity fluid stream to stay centered in that stream to center the head end of an outward opening check valve within an orifice opening concentric with the centerline of the valve head when seated. With the valve head so centered when lifted from its seat, a symmetrical annular orifice of controlled restriction is formed.
Another objective is to provide a method for adjusting the assembled spring load in an outward opening valve assembly by determining the total thickness of means to be selected for assembly between the spring end and a side of the pin opening in the valve.
Also, for the outward opening valve requiring a lift stop, an objective is to provide a method for determining how far the check and spring end should move to provide an opening area around the check with a specified delivery rate capability. This method includes determination of the height of a stop surface on parts to be assembled between the spring end and pin opening for production uniformity in flow rate characteristics at such lift.